Rocket propulsion by reacting



Patented June 21, 1949 ROCKET PROPULSION BY REACTING ALKYL-SUBSTITUTED MONONUCLEAR AROMATIC AMINES AND NITRIC ACID Victor L. King, Bound Brook, N. J., assignor to American Cyanamid Company, New York, N. Y.;,' a corporation of Maine No Drawing. Application August 9, 1943, Serial No. 497,999

4 Claims. (Cl. 60-355) This invention relates to a reaction propulsion method, and more particularly to a method for generating power by ejecting a stream of combustion products at high velocities. Rocket motors of the type used for propelling airplanes are the most important field in which this method of propulsion is employed at the present time, although the invention in its broader aspects is not limited to this field.

Modern rocket motors of the type now in use to give an accelerated take-off or accelerated speeds in airplanes consist of a suitable housing provided with pairs of'jets adapted to inject a fuel and an oxidant, respectively. The combustion of these two materials creates a mass of hot, burning gases which are ejected at high velocity through a suitable orifice, the reaction from this ejection providing the propulsive force. Such motors are of great potential value in assisting the take-off of seaplanes, since additional power is needed to overcome the skin friction of the water against the hulls of such planes. They are also of great value in assisting the take-oil! of heavily loaded land planes, since it is well-known that only a fractionof the power in a modern airplane is used in flight, as compared with that necessary to lift the plane from the ground under ordinary take-of! conditions.

In order to assist the take-off of airplanes it is of utmost importance to have a rocket fuel which will ignite immediately and with certainty, as the plane wouldbe almost certain to crash if the rocket motor failed to flre. For this reason a self-igniting fuel mixture is greatly preferred to one which must be ignited by a spark or by compression, as in ordinary internal combustion engines. It is a principal object of the present -invention to provide a reaction propulsion method which is both instantaneous in action and certain in character, so that power failure is reduced to a minimum.

I have found that the alkyl-substituted mononuclear aromatic amines containing one or more alkyl substituents will ignite spontaneously upon admixture with strong nitric acid to produce a stream of combusion products capable of developing high velocities in a rocket motor. I have also discovered that this class of compounds possesses a number of other extremely important properties which cause the members thereof to be well-suited for use in propulsive fuels. The

compounds of this class have very low freezing points and will therefore remain fluid at the low temperatures encountered in severe winter weather and during high altitude flights. More- 2 over they are soluble in low-boiling hydrocarbon fuels such as gasoline and light fuel oil and will form solutions therein that do not freeze or thicken at low temperatures. Solutions of this type containing at least 20% by volume of alkylsubstituted mononuclear aromatic amines will ignite spontaneously upon admixture with strong nitric acid, and are therefore suitable for use as a rocket fuel instead of the pure aromatic compounds themselves.

The class of alkyl-substituted mononuclear aromatic amines includes those compounds containing one or more alkyl substituents on the amino nitrogen and those containing one or more alkyl substituents on the aromatic nucleus as well as those in which both an amino nitrogen and the aryl nucleus are substituted by aliphatic radicals. Typical compounds possessing the advantages enumerated above are the lower N- aliphatic mononuclear aromatic amines such as monoand dimethylaniline and monoand diethylaniline. These compounds may be employed in the pure state, but the crude mixtures obtained .by their ordinary methods of preparation may be used with equally good results. Thus, for example, crude monoethylaniline as prepared by the autoclave process has the following composition:

Per cent I i-monoethylaniline 55 Aniline 30 35 Residue 10-15 Per cent N-monoethylaniline 60 Aniline 30 Residue 10 The residue consists principally of N,N-diethylaniline, but contains small quantities of nuclear- I substituted anilines.

Crude monomethylaniline prepared by the autoclave process contains about 40% N-monomethylaniline, about 20% N,N-dimethylaniline and about 40% aniline. All three of these mixbustion agents are the lower nuclear-substituted alkyl anilines such as the toluidines and the mixed xylidines obtained by the reduction of nitrated toluene and xylene mixtures. Other typical compounds are the N-alkyl xylidines and toluidines such as N-monoand dimethyl metaand para-toluidines and alkyl-substituted phenylene diamines, such as N,N'-dipropyl, dibutyl and diamyl para-phenylene diamines. These compounds may be used as such, or in admixture with each other, or in admixture with other igniting and combustion agents such as aniline, gasoline, Diesel fuel oil, #2 fuel oil, benzene, or mixtures thereof.

I1- order to obtain rapid and positive spontaneous ignition of the aromatic amines it is necessary to use strong nitric acid, and this term is intended to designate nitric acid containing not more than about of water. As is illustrated in detail in Example 5, bleached nitric acid having a strength of about 95% ENG: is about the weakest acid that will give reliable results, but the quenching effect of larger amounts of water can be compensated to a limited extent by the presence of N02. Accordingly, nitric acid of about 96-99.5% HNO: content or fuming nitric acid containing not more than 8-10% of water are the proper types of acid to use in conjunction with the igniting agents of the present invention, and these are the materials designated by the term strong nitric acid.

From the foregoing it will be seen that the process of the present invention consists in the generation of rocket propulsion by impinging a jet of strong nitric acid upon a similar jet of a fuel containing an aliphatic-substituted mononuclear aromatic amine, or by commingling the oxidizing agent and fuel by any other suitable means. The ratio of strong nitric acid to fuel will depend upon the type of fuel and upon the strength of the acid used, but in general the ratios should be such as to provide sumcient nitric acid to oxidize at least 70-80% of the fuel. The alkaryl amine may be used as a fuel or it may be dissolved in a hydrocarbon fuel to function as an ignitin agent therefor, with or without the addition of aniline or other additional combustion agents. In this case the amount of alkaryl amine may vary from 10% to 50% by volume of the total quantity of fuel, the higher concentrations being used when the rocket motor is first fired and a somewhat leaner mixture being employed during continued operation. Alternatively, the motor may be started by the use of a straight alkaryl amine or mixture thereof with aniline or other aromatic amines as the sole igniting agent and carburant and then operated with a straight hydrocarbon fuel or with a similar fuel containing a relatively small quantity of aralkyl amine as an igniting agent.

The rapidity of ignition and flame formation of the aliphatic-substituted mononuclear aromatic amines can be demonstrated by a cup test in which a strong nitric acid is poured into a dish containing the amine or solution thereof under test. A large number of such tests have shown that the results obtained thereby are reproducible and will give a reliable indication of the operation of similar mixtures in a rocket motor. Accordingly, cup tests of mixtures illustrative of the present invention are described in the following examples, it being understood that similar results are obtained when the same ingredients are sipplied to the jets of a rocket motor as described a ove.

The invention will be illustrated in greater detail by the following specific examples. It should be understood, however, that although these examples may describe some of the more specific features of the invention, they are given primarily for purposes of illustration and'the invention in its broader aspects isnot limited thereto.

Example 1 The efficacy of N-ethyl aniline, both alone and in admixture with low-boiling hydrocarbon fuels, was tested by a cup test in which suitable quantitles of strong nitric acid were poured into a 4- inch porcelain evaporating dish containing the igniting agent.

(a) 15 cc. of red fuming nitric acid (sp. gr. 1.60) were poured into 10 cc. of the N-ethyl aniline. There was an immediate brightflash followed by violent combustion with evolution of heavy white fumes.

(b) 10 cc. of the same acid were poured into a solution of 3 cc. of N-ethyl aniline in '7 cc. of #2 fuel oil. An immediate bright flash was followed by rapid burning.

(c) 10 cc. of red nitric acid analyzing 81.4% HNOa, 4.1% H20 and 15.5% dissolved N0: were poured into 7 cc. of the monoethyl aniline. An audible flash resulted, followed by a hissing flame.

(d) 10 cc. of 99.5% nitric acid were poured into 7 cc. of the fuel oil solution described in (b). There was a large bright flame after about 0.25 second or less, and the mixture burned vigorously.

Example 2 15 cc. of 99.5% nitric acid were poured into 10 cc. of N-methyl aniline as described in Example 1. There was an instant bright, audible flame which burned with evolution of brown fumes. The same result was obtained with N-isopropyl aniline and with N,N-dimethylaniline.

Example 3 xylidines obtained by the reduction of a nitroxylene mixture.

Example 4 Aniline itself is a good igniting and combustion agent for propulsive fuel mixtures, but its freezing point (-6 C.) is too high for use. I have discovered, however, that the addition to aniline of aliphatic-substituted mononuclear aromatic amines such as Z-cymidine, mixed xylidines, N- methyl aniline, N-ethyl aniline and the like will produce combustion agents of much lower freezing points having as ood or better igniting properties than aniline itself.

Another very serious disadvantage of aniline is its relatively low solubility in hydrocarbon fuels such as diesel fuel, gasoline and fuel oil. Thus. for example, a mixture of 10 parts by volume of aniline with parts by volume of light fuel oil forms two immiscible layers. A 10% aniline-90% by volume gasoline solution separates into two Percent by volume Gasoline 6 acid that will give reliable results. However, N: and N204 may also be used, and the quenching effect of water in acids weaker than 95% may be compensated to a limited extent by the presence of N02. This was shown by testing the following compositions:

Eflect on Cooling N-Methyl Aniline:

Turbid at 36 0., Freezes at 40 Does not freeze at -48 0.

Mixed xylidines:

The freezing points of representative mixtures containing aniline are as follows:

50 at 85 0., Two layers at 75 Turbidg t -85 0., Does not freeze 90 Turbid at 50 0., but does not been.

50 Does not separate at 50 0.

No BNO Hi0, I N0:

' percent percent percent I Commercial bleached 95- mm ma, plant production.

These acids were tested in the cup test against a crude vapor-phase aniline having the composition previously described and also against mixtures of this material with hydrocarbon fuels. In all cases cc. of the acid were poured into Percent by volume Other Component 's. Point Remarks Aniline 5 Mixed xylidines 9 I xylidines -l1. 5 M 361 xylidin --13 M xer xylidin 28 M X xylhilnm: 40 5 50 Mixe xylidines (-48 15 2-cyml dine. i3 2-cym dine. -30 50 Z-cyml dine. -42 20 N-ethyl anilin -l4 5 to l8. 5 No deilnite F. P. N-ethyl anilin -25 to B Do. 20 N-methyi anilin --13 5 to 14 Do. 40 N-metbyl anilin -23 fibers F P. 10 l0. 5 0. l5 13. 2 Do. 23 Equal Volumes 0! N-Ethyl Aniline, Mixed xylidines and 2-Oy'mldine -(5 go. o. 36 Do.

It is evident from these figures that the alkylsubstituted 'anilines may be used as such or in admixture with aniline as igniting and combustion agents in gasoline, diesel fuel, light fuel oils, benzene and other low-boiling hydrocarbons even in severe winter weather and at the low temperatures encountered in high-altitude flights. Typical results are shown by the following tests, which were made by pouring 2 parts by volume of 9'7 HNOa into 1 part of the composition under test, as described in Example 1, the parts being by volume:

(a) Anfline ignited vigorously with copious flame formation (b) Aniline mixed xylidines 40%. v orous than aniline.

(c) Aniline 50%, N,N-dimethylanillne 25%, nitrobenzene 25%. Results equal to aniline.

(d) Aniline 50%, mixed xylidines 25%, nitrobenzene 25%. Better than (b).

(e) Gasoline 80%, benzene 10%, aniline 5%,

More

' nitrobenzene 5%. Most vigorous of all.

Example 5 Strong nitric acid should be used to obtain reliable and rapid ignition of the mononuclear aromatic amines and their mixtures with low-boiling hydrocarbons. Bleached nitric acid having a strength of 94-95% HNO: is about the weakest 7 cc. of the igniting agent The results are shown in the following table:

Nuclear substituted anilines containing a number of alkyl radicals are very ef' ctive igniting agents. Thus, for example, 7 cc. of a mixture of pseudocumidine (2,4,5 trimethylaniline) and mesidine (2,4,6-trimethylaniline) ignited upon 7 addition of 10 cc. of ordinary 95% nitric acid with a time lag of only 0.4 seconds and burned with a bright flame.

Example 7 A pair of rocket motor jets having internal diameters of V 4" and set at an angle of 80 were fed with 99.5% nitric acid and with N-monoethylaniline, respectively, under pressures of 7 lbs. per square inch. The mixture ignited immediately at the jets and burned with a big flame that was propelled violently against a metal shield five feet distant.

What I claim is:

1. A rocket propulsion method which comprises generating an ignited propulsive charge by commingling with strong nitric acid a volatile hydrocarbon having dissolved therein 10-50% of an alkyl-substituted mononuclear aromatic amine and ejecting the burning charge at high velocity.

2. A rocket propulsion method which comprises generating an ignited propulsive charge by commingling with strong nitric acid a volatile hydrocarbon having dissolved therein 10-50% of an N-aliphatic mononuclear aromatic amine and ejecting the burning charge at high velocity.

3. A rocket propulsion method which comprises generating an ignited propulsive charge by commingling with strong nitric acid a volatile hydrocarbon having dissolved therein 10-50% of an N-alkyl aniline and ejecting the burning charge at high velocity.

4. A rocket propulsion method which comprises generating an ignited propulsive charge by commingling with strong nitric acid a volatile hydrocarbon having dissolved therein about 10-50% of a mixture of aniline and N-ethylaniline and e] ecting the burning charge at high velocity.

VICTOR L. KING REFERENCES CITED The following references are of record in the file of this patent:

UNITED' STATES PATENTS OTHER REFERENCES Journal of the Chemical Society, London, 1942, pages 584-585. 

